1. Field of the Invention
This invention relates to a highly flame retardant plasticized polyvinyl chloride compound (PVC) further characterized by an absence of brittleness at low temperatures, and substantial flexibility such as required for PVC formed jackets and insulation for wire and cable products and sheets often used, for example, as roof sheathing upon which shingles or other roof covering is laid.
2. Description of the Related Art
PVC compounds (PVC) are a well known class of thermoplastic polymers which exhibit excellent chemical and corrosion resistance, physical and mechanical strength, and electrical insulative properties. Unplasticized versions of PVC are inherently flame resistant and rigid PVC compounds require only additional antimony trioxide to achieve a high level of flame retardancy. However, when flexible forms of PVC are required, the addition of plasticizers result in increased flammability of PVC. Conventional PVC is also apt to produce excessive smoke when ignited.
Both triaryl and diaryl alkyl phosphate esters have been used to improve the flame retardancy of PVC. High flame retardant demands for more stringent flexible PVC applications, such as outer jackets and insulators for plenum wires and cables, for sheets used in the construction industry, for example, as roof sheathing upon which shingles or other roof coverings are laid, as well as for flexible coatings applied to fabrics, have required improvements in the flame retardant plasticizers incorporated in these compounds. The additional of dialkyl tetrahalophthalates such as dioctyl tetrabromophthalate or di-2-ethylhexyltetrabromophthalate have been able to achieve exceptional thermal stability with exceptional flame retardancy. However, the low temperature flexibility of PVC compounds is compromised with the addition of such compounds.
It is known that flame retardant synergy is exhibited by certain brominated and chlorinated compounds. (By use of the term "flame retardant synergy" it is meant that the action of two or more substances achieve an effect of which each is individually incapable.) For example, a paper entitled Bromine-Chlorine Synergy To Flame Retard ABS Resins, by Seunghee Yun and Hyunkoo Kim of Miwon Petrochemical Corporation, presented at the New Developments and Future Trends in Fire Safety On A Global Basis International Conference, March 1997, discusses mixtures of DECHLORANE.TM. PLUS, a product of Occidental Chemical Corporation, and TBBA (Tetrabromobisphenol A), or FF-680 (Bis(Tribromophenoxy)Ethane) to produce acrylonitrile butadiene styrene (ABS) resins having improved flame retardant characteristics. However, the Yun and Kim results refer to ABS, a rigid plastic used in electrical component housings (e.g. TV cabinets and computer casings). Yun and Kim use the chlorinated substance Dechlorane Plus to increase the rigidity of the resultant ABS. Such rigidity would be a serious flaw in PVC formed jackets and insulation for wire and cable products. Improvement of flame retardant properties, as well as improvement of low temperature flexibility and decreased smoke generation, has not heretofore been known when the type of brominated and chlorinated compounds of the present invention are used in PVC compounds. The principal object of the present invention, therefore, is to provide a highly flame retardant plasticized PVC based on the discovery that improved low temperature flexibility can be achieved by adding to PVC dialkyl tetrahalophthalate mixtures of the type hereafter described.
Dialkyl tetrahalophthalates are produced from the reaction of tetrachlorophthalic acid or anhydride and/or tetrabromophthalic acid or anhydride with C.sub.1 -C.sub.18 alkanols. The production of dialkyl tetrabromophthalate and dialkyl tetrachlorophthalates is well known in the field. Numerous processes have been described for the preparation of dialkyl phthalates by esterification of various alcohols with phthalic anhydride or acid in the presence of acidic catalysts, such as sulfuric acid, phosphoric acid, toluene sulfonic acid, and methane sulfonic acid. For example, Spatz et al. (I & EC Product Res. and Dev. 8: 391, 1969) discloses the preparation of di-2-ethylhexyl tetrabromophthalate using phosphoric acid catalysis. Nomura et al. (published Japanese Patent Application No. 50-05701, 1975) describes the use of tetraalkyl titanates in the presence of alkali metal salt to prepare dialkyl tetrabromophthalates. Sagara et al. (U.S. Pat. No. 4,284,793) discloses a method for producing plasticizers with low residual titanium, in which phthalic anhydride is reacted with an alcohol in the presence of a titanate catalyst. The resultant ester is treated with a solid alkali, such as sodium carbonate, and adsorbing agent(s) in the absence of water. Watanable et al. (U.S. Pat. No. 4,304,925) discloses a process for purifying esters, such as those formed from phthalic anhydride and ethyl hexyl alcohol, when organotitanium compounds are used as catalysts, where water is added to the esterification mixture and the mixture is heated. Mamuzic et al. (U.S. Pat. No. 4,754,053) discloses the preparation of tetrabromophthalate diesters using sodium carbonate decahydrate as an essential part of the process. Bohen et al. (U.S. Pat. Nos. 5,049,697 and 5,208,366) disclosed a process for the preparation of dialkyl esters of polyhaloaromatic acids catalyzed by the use of various organometallic catalysts, such as organotitanates, as well as organo-tin, antimony and zirconium compounds. However, these patents do not disclose nor suggest mixing tetrabromophthalate and tetrachlorophthalate for the purpose of improving low temperature flexibility of PVC.
Accordingly, the primary object of this invention is to improve the low temperature flexibility of highly flame retardant plasticized PVC compounds by incorporating into PVC, according to the discovery of the invention, dialkyl tetrahalophthalate mixtures containing both tetrabromophthalates and tetrachlorophthalates.
A further object of this invention is to decrease the smoke generation character of PVC.
Another object is to provide an improved PVC approved for use in products such as insulation, jackets, coatings, and sheeting.
Other objects and advantages will be more fully apparent from the following disclosure and claims.